Microsporogenesis, microgametogenesis, and pollen grain morphology of Fouquieria fasciculata (Fouquieriaceae, Ericales)

Background: Embryology of the male reproductive structures in Fouquieriaceae has been poorly studied. The ontogeny of the anther wall, microsporogenesis, microgametogenesis, and pollen morphology were described in detail for Fouquieria fasciculata. Questions: How microsporogenesis and microgametogenesis are carried out in Fouquieria fasciculata? How is the morphology of mature pollen grain? Study species: Fouquieria fasciculata (Fouquieriaceae). Study site and date: Río Estórax Canyon, near the El Plátano, Querétaro, Mexico. Methods: Floral buds and flowers at different stages of development were collected and processed for further analysis with light and scanning electron microscopy. Results: The development of the anther wall is of Dicotyledonous type. The anther wall consists of a single-layered epidermis covered by a thick cuticle, an endothecium with U-shaped fibrous thickenings, one middle layer and a secretory tapetum with uni or binucleate cell. Two orbicules types were characterized: doughnut-shape orbicules and aggregated orbicules with ruminate appearance. Microsporogenesis is successive, the microspore tetrads are tetrahedral. Pollen grains are prolate, tricolporate with reticulate-heterobrochate exine, and are shed in the two-celled stage. Conclusions: This research is the first comprehensive study of male structures ontogeny of Fouquieriaceae. Remarkable features were described in Fouquieria fasciculata, such as the differentiation of a secretory tapetum and the presence of orbicules, which are described for the first time and contribute to characterize the embryology of Fouquieriaceae.